1. Field of the Invention
The present invention relates to air intake systems for carburetor-equipped internal combustion engines, and, more particularly, to the linkage for a continuously adjustable flapper-type air mixing valve which is controlled by a pneumatic membrane actuator and a wax thermostat, to mix cold raw air with preheated raw air, for an optimal raw air temperature, under changing operating conditions.
2. Description of the Prior Art
The use of a pivotable flapper as a flow proportioning valve at the junction point between a cold air intake duct and a warm air intake duct has enjoyed widespread acceptance in connection with control systems which are designed to maintain an optimal raw air intake temperature for carburetor-equipped internal combustion engines. This flapper is normally so arranged that in each of the two pivoting end positions it closes off one of the two raw air intake ducts, while fully opening the other, admitting variable amounts of cold and preheated raw air, respectively, in all intermediate positions.
It has also become common practice to use for the positioning of the flapper a pneumatic membrane actuator which is driven by the negative pressure which results from the aspirating action of the pistons, and which is tapped downstream of the main throttle of the carburetor.
It has further been suggested that the flapper positioning action of the membrane actuator be combined with the adjustment action of a wax thermostat sensing the air temperature in the cold air intake duct. The interaction of this wax thermostat with the flapper may be in the form of a movable flapper stop which, under certain operating conditions, prevents the flapper from fully closing the warm air intake duct, or the wax thermostat may form a part of the drive connection between the membrane actuator and the flapper. In the latter case, the wax thermostat increases or decreases the effective length of the drive connection, in response to changes in the ambient temperature. An arrangement where the wax thermostat serves as an adjustable flapper stop is disclosed in U.S. Pat. No. 4,161,930. An arrangement where the wax thermostat forms part of the drive connection between the membrane actuator and the flapper is disclosed in U.S. Pat. No. 4,144,857.
In the last-mentioned control system, in which the wax thermostat forms part of the drive connection, the pneumatic membrane actuator and the thermostat are arranged to form a preassembled, preadjusted drive unit. The wax thermostat is carried by a frame extension of the actuator housing, the thermostat housing bearing against a spring, and the thermostat drive pin engaging the drive disc of the membrane actuator. The housing of the wax thermostat thus executes longitudinal movements in the direction of the flapper, these movements reflecting the combined actions of the negative pressure in the carburetor and of the temperature sensing wax thermostat. A pivot connection between the thermostat housing and the flapper transmits the movements of the former to the latter.
A prior art suggestion of a linkage between the housing of the wax thermostat and the pivotable flapper involves the use of a round rod having one extremity permanently attached to the bottom of the thermostat housing and the other extremity angled off and engaging a matching aperture in the flapper. This arrangement, while being operationally satisfactory, has certain shortcomings with regard to the cost of mass production and assembly.